Update "Router Events" deprecation guide

[locks]

The following guide https://deprecations.emberjs.com/v3.x/#toc_deprecate-router-events uses Route#transitionTo–which is now deprecated–in the "after" code sample. Should this be updated to use the Router service? The "Router Events" deprecation is 20 minor versions earlier, but I believe the Router service was already available, and it skip triggering one deprecation if we show examples with the Router service.

[jenweber]

One way to tackle this is to run the example through the octane codemod and see what happens, instead of rewriting by hand.

Since this deprecation was introduced in 3.4, prior to Octane, and is removed for 4.0, we want to show both styles of examples - one that works pre-Octane, and one that works after.

[kategengler]

The willTransition and didTransition that are removed were on the Router class https://deprecations.emberjs.com/v3.x/#toc_deprecate-router-events

The deprecation guide for the until 5.0 deprecation is https://deprecations.emberjs.com/v3.x/#toc_routing-transition-methods